Exhalation Valve for Mask

An apparatus comprising an exhalation valve that remains closed until opened in response to exhalation pressure caused by a pulse of exhaled air, wherein said exhalation valve comprises:

• a cover, a base that engages said cover, a valve body that is between said cover and said base, and a cantilevered diaphragm having a clamped region and a valve face, said valve face comprising a plurality of regions, each of which defines a moment arm, wherein said plurality of regions comprises a particular region that defines a moment arm that is longer moment arms of all other regions, wherein said clamped region is clamped at said valve body, wherein said valve face is free to deform in response to said exhalation pressure, wherein said valve body comprises:
• a valve seat that is disposed on said valve body and that faces said valve face and a plurality of vanes, said vanes being configured to cause a pressure field that results from said exhalation pressure to have an average pressure gradient that points toward said valve seat and said particular region of said valve face, and wherein, in the absence of exhalation-induced torque at said valve face that is above a threshold, said valve face contacts said valve seat and closes said exhalation valve, and wherein, in response to exhalation-induced torque above said threshold, said valve seat lifts off said valve seat and opens said exhalation valve.